Coatings comprising self-stabilized lattices prepared in a aqueous carrier

ABSTRACT

An aqueous coating composition comprising a graft copolymer characterized by carboxylic-acid or amine functional macromonomers attached at a terminal end thereof to a polymeric backbone, wherein the macromonomers are grafted in an aqueous carrier in which the carboxylic-acid or amine functional groups have been neutralized. Such compositions provide improved properties for an automotive finish.

CROSS-REFERENCE TO RELATED APPLICATION

This is a 371 application of PCT/US95/05767, filed on May 9, 1995 whichis a continuation of U.S. Ser. No. 08/246,195 filed on May 19, 1994, nowabandoned.

TECHNICAL FIELD

This invention relates to an improved aqueous composition for coating avariety of substrates. In particular, this invention is directed to acoating composition comprising a graft copolymer, referred to as aself-stabilized latex, having neutralized carboxylic-acid or aminefunctionality in a graft segment thereof which stabilizes the aqueousgraft copolymer dispersion. The invention involves preparing the graftcopolymer in an aqueous carrier.

BACKGROUND OF THE INVENTION

Automobiles and trucks receive exterior finishes for several well knownreasons. First, such finishes provide barrier protection againstcorrosion. Second, consumers prefer an exterior finish having anattractive aesthetic finish, including high gloss and excellent DOI(distinctness of image).

A typical automobile steel panel or substrate has several layers offinishes or coatings. The substrate is typically first coated with aninorganic rust-proofing zinc or iron phosphate layer over which isprovided a primer which can be an electrocoated primer or a repairprimer. Optionally, a primer surfacer can be applied to provide forbetter appearance and/or improved adhesion. A pigmented basecoat orcolorcoat is next applied over the primer. A typical basecoat orcolorcoat comprises a pigment, which may include metallic flakes in thecase of a metallic finish. In order to protect and preserve theaesthetic qualities of the finish on the vehicle, it is well known toprovide a clear (unpigmented) topcoat over the colored (pigmented)basecoat, so that the basecoat remains unaffected even on prolongedexposure to the environment or weathering.

Coating compositions comprise one or more film-forming polymers. Mostcommonly, acrylic polymers are linear in structure and cure, uponapplication, by reaction with crosslinking agents. However, the use ofnon-linear graft copolymers has been disclosed. For example, U.S. Pat.No. 4,801,653 to Das et al. describes the use of hydroxy functionalgraft copolymers. Das et al. disclose grafting by a condensationreaction between epoxy groups of a glycidyl ester, contained in anacrylic polymer, and carboxy groups on at least a portion of vinylmonomers which are polymerized in the presence of the acrylic polymer.

In preparing graft polymers in general, various living polymerizationmethods have been disclosed for obtaining functional ended polymers byselective termination of living ends. Such functionally ended polymersmay subsequently be attached to another polymer, that is, as so-calledmacromonomer "arms" on a polymeric backbone to form a comb or graftcopolymer. Webster, in "Living Polymerization Methods,"251 SCIENCE 887(Feb. 22, 1991) generally discloses living polymerization methods forpreparing architectural forms of polymers, including graft and combcopolymers.

U.S. Pat. No. 4,680,352 to Janowicz et al., U.S. Pat. No. 4,722,984 toJanowicz, and PCT WO 87/03605 disclose the use of cobalt (Co) chelatesas chain transfer agents in free radical polymerization. The latterpatents disclose that macromonomers prepared by cobalt chain transfercan be polymerized to produce graft copolymers which are useful incoating and molding resins, including high solid finishes and aqueous orsolvent based finishes. The use of such polymers, however, have so farfound only limited use in the automotive finishes area, as for exampledisclosed in U.S. Pat. No. 5,010,140.

The present invention relates to aqueous coating compositions. Theevolution of environmental regulations has led to the need for productswith lower volatile organic content (VOC). However, it is far fromtrivial to develop aqueous products with desirable properties forautomotive finishes. As mentioned above, such finishes must be highperformance in terms of aesthetic qualities and durability.

Water dispersible polymers are well known in the art and have been usedto form waterbased coating compositions, pigment dispersions, adhesivesand the like. Graft copolymers containing carboxyl groups and thepreparation of these polymers is shown in Japanese Laid Open PatentApplication (Kokai) No. 1-182304 dated Jul. 20, 1989. This referenceshows graft copolymers that have carboxyl groups and discloses sidechains from acrylic and methacrylic acid that have hydrophilicproperties. This reference further teaches the use tertiaryalcohol-based ester units of acrylic or methacrylic acid to form amacromonomer which is used to form a graft copolymer and then ishydrolyzed to form carboxylic-acid groups on the polymer. The processtaught by the reference is an inefficient process which does not formpure graft copolymer but results in a mixture of graft copolymer and lowmolecular weight components that are detrimental to pigment dispersionsformed from the graft copolymer and finishes formed from such acomposition.

BASF EP 0363723 describes an acid-functional acrylic copolymerdispersion for use in an original equipment manufacturer (OEM) clearcoat to be crosslinked with a melamine formaldehyde binder. The acryliccopolymer is prepared in a solvent in a two-stage process where thehydrophilic part (acid-functional monomer) is concentrated in one of thetwo stages. The overall copolymer is afterwards neutralized with anamine and dispersed in water. The difference between a one stage productis the solids/viscosity relation being most favorable for the two stageacrylic. A disadvantage of this technology is the fact that thehydrophilic part needs to be over 60% of acid functional monomer whichcould give problems in humidity resistance. The present method has theadvantage that acid or amine functional copolymer macromonomers could beused which provide advantages in terms of humidity resistance,appearance, and lower minimum film-forming temperatures. Also, little tono cosolvent is needed to prepare the graft copolymer dispersion.Another disadvantage is that introducing hydroxy functional monomers inthe hydrophilic part has strong negative effects on the solids/viscositybalance. Finally, another disadvantage is that the two stage acrylicneeds to be prepared in cosolvents.

Bayer patents EP 0218906 and EP 0324334 describe the synthesis ofhydroxy-acid functional acrylic copolymers prepared in solution beforeneutralizing with an amine and dispersing in water. This has thedisadvantage of the solids/viscosity balance referred to above.

Bayer EP 0334032 describes the synthesis of an acid-functional urethaneoligomer which is used to stabilize a waterborne acrylic copolymerdispersion. This technology does not allow hydroxy-functional groups(for crosslinking) in the hydrophilic stabilizing part.

AKZO U.S. Pat. No. 5,098,947 describes urethane modified acryliccopolymer dispersions for waterborne coatings. This technology is alsolimited by the use of cosolvents in which the urethane part is prepared.

As indicated above, the aqueous finishes disclosed in the prior art havesignificant disadvantages, for example, in terms of humidity resistance,acid resistance, durability, appearance and other properties. Thus, theproblem of developing aqueous finishes with improved properties remainsand has been the subject of considerable research and development in theautomotive coatings industry.

The present invention offers significant advantages. Acid or aminefunctional macromonomers can be used which provide improved humidityresistance and appearance. Lower minimum film-forming temperatures maybe used. Little to no cosolvent is needed to prepare the graft copolymerdispersion. The acid-functional or amine-functional graft can also behydroxy functional for crosslinking with the amino formaldehyde and/orthe (un)blocked polyisocyanate crosslinkers.

SUMMARY OF THE INVENTION

The present invention relates to a waterborne curable compositioncomprising a blend of a graft copolymer, which contains activefunctional or reactive groups, and a curing agent. The graft copolymeris prepared from an acrylic copolymer macromonomer comprising at least10% by weight of polymerizable alpha-beta ethylenically unsaturatedmonomers with carboxylic or amine functionalities and a weight averagemolecular weight (MW) of 500 to 30,000. About 2-98% (by weight) of themacromonomer is copolymerized with 98-2% of a blend of other alpha,beta-ethylenically unsaturated monomers to form a graft copolymer with aMW of at least 3000. The macromonomer is neutralized with an amine oracid or other neutralizing agent before dispersing in the aqueouscarrier and then forming the graft copolymer by copolymerizing thebackbone monomers in the presence of an aqueous dispersion of themacromonomers.

Suitably, the curing agent comprises a melamine formaldehyde oralkylated melamine formaldehyde compound or a blocked or unblockedisocyanate compound in a one-package system or an isocyanate compound,preferably a water-dispersible polyisocyanate, in a two-package system,or other crosslinking agents such as epoxies, silanes, carbodiimides,etc. able to react with the functional groups present on the graftcopolymer.

It has been found that improved aqueous or waterborne coating systemsare obtained by using these graft copolymers. Such compositions have theadvantage of providing excellent coating properties desirable for anautomotive finish. The present invention is directed to a coatingcomposition comprising:

(a) from about 5 to 98 percent, based on the weight of the binder, of agraft copolymer having a weight average molecular weight of 3,000 to500,000 comprising:

(i) 2 to 98 percent by weight of the graft polymer of a polymericbackbone comprising ethylenically unsaturated monomers, and

(ii) 98 to 2 percent, by weight of the graft polymer, of macromonomersattached to said polymeric backbone at a single terminal point of eachmacromonomer, said macromonomers comprising from about 10 to 100percent, based on the weight of the macromonomer, of polymerizedethylenically unsaturated monomers all containing carboxylicfunctionality, or instead amine functionality, and having a weightaverage molecular weight of about 500-30,000, such that themacromonomers are water soluble or dispersible when neutralized, themacromonomer comprising methacrylate monomeric units having been reactedin the presence of a cobalt chelate chain transfer agent;

(b) 2 to 50 percent, based on the weight of the binder of a crosslinkingagent which reacts and crosslinks with said carboxylic or aminefunctionality in said graft polymer; and

(c) 40 to 90 percent by weight, based on the weight of the composition,of an aqueous carrier comprising 80 to 100 percent water; wherein saidgraft copolymer is the polymerization product, in an aqueous carriercomprising 80 to 100 percent water, of said macromonomers and saidmonomers comprising said backbone, and wherein said carboxylic or aminefunctionality has been at least partially neutralized to form a stabledispersion or solution, with the backbone mostly in particle form, inaqueous carrier.

This above-described graft copolymer may also be employed together witha curable linear or branched film-forming polymers or binder materials,in various proportions. For example, the composition may comprise linearor branched hydroxy-functional acrylic, polyester, or polyurethanecopolymers. Further binder materials, in relatively minor amounts,include, for example thickeners, adhesion promoters, etc.

The present composition is especially useful for finishing the exteriorof automobiles and trucks and parts thereof. The present composition,depending on the presence of pigments and other conventional components,may be used as a primer, primer surfacer, basecoat, and/or clearcoat. Itis especially advantageous for use in an aqueous clearcoat. Theinvention also includes a process for coating a substrate with the abovecoating composition. The claimed composition further includes asubstrate having adhered thereto a coating according to the abovecomposition. The graft copolymer and the process for making the graftcopolymer are also part of this invention.

The present invention offers several significant advantages. First,graft copolymers with acid or amine groups concentrated in one segmentrequire less acid or amine to get a stable dispersion, thus leavingfewer moisture sensitive carboxylic or amine groups in the finalcoating.

Second, standard emulsions are stabilized by surfactants which besidesremaining in the film as moisture sensitive residues, migrate to thecoating interfaces and generate weak boundary layers which lead to pooradhesion and delamination. The surfactants also stabilize foam formed bytrapped air during spraying, leading to pinholing. The compositionsaccording to the present invention can be made with lesser amounts ofsurfactants, preferably no surfactants.

Third, standard emulsions for which water is a non-solvent, needconsiderable solvent to allow coalescence (film formation) after beingapplied to a surface. This leads to higher VOC. In the presentinvention, the hydrophilic macromonomers which are on the surface of theself- stabilized lattices are plasticized by the water and allow filmformation with little or no solvent, thus allowing coating compositionsto be formulated with much lower VOC. These and other advantages of theinvention can be better understood by reference to the followingdetailed description of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The waterborne coatings of the present invention comprise anacrylic-based binder system in an aqueous base. This binder systemcomprises, in its overall concept, a water soluble or dispersibleacrylic graft copolymer which is formed by free radical initiatedcopolymerization of 2-98% (by weight) alpha-beta unsaturated monomers inthe presence of an acrylic macromonomer. The acrylic macromonomer has anaverage number molecular weight (N) of between 500 to 30,000 andcontaining at least 10% of an acid or amine functional alpha-betaunsaturated monomer. By the term "acid or amine" is meant alternativelyone or the other, not both aggregately, since cationic or anionic, notamphoteric systems are contemplated. After at least partialneutralization of the carboxyl groups or amine with, for example, anamine in the case of carboxy groups, these acrylic resins form stablesolutions or dispersions in water. These resins form particles, eitheralone or in aggregate with other such resins in the composition, inwhich the macromonomers are relatively hydrophilic and hence soluble ordispersible in the aqueous carrier, and the polymeric backbone (to whichthe macromonomers are attached) is relatively water insoluble. Suchparticles may be crosslinked or uncrosslinked, for example by means ofdiacrylate monomeric units, and suitably have an average particle sizeof 50 to 1000 nanometers (nm), preferably 100 to 250 nm.

The acrylic macromonomer is preferably prepared using a free radicalinitiator in a solvent with a Co (II) or Co (III) chelate chain transferagent and contains 10 to 100 percent, preferably 20 to 40 percent, byweight of an functional monomer, e.g., acrylic acid, methacrylic acid,maleic acid, and itaconic acid or their anhydrides (which can behydrolyzed to the acid after polymerization). Amine-functional monomersinclude t-butylamino ethyl methacrylate, diethyl (or dimethyl) aminoethyl acrylate, diethyl amino ethyl methacrylate, and the like.Preferably the macromonomer is based on methacrylic acid or dimethylamino ethyl methacrylate.

In general, the total polymeric and oligomeric components of a coatingcomposition are conventionally referred to as the "binder" or "bindersolids" and are dissolved, emulsified or otherwise dispersed in theaqueous liquid carrier. The binder solids generally include all thenormally solid polymeric components of the composition. Generally,catalysts, pigments, or chemical additives such as stabilizers are notconsidered part of the binder solids. Non-binder solids other thanpigments usually do not amount for more than about 10% by weight of thecomposition. The coating composition of the present invention suitablycontains about 10-90%, more typically 50-70% by weight of the binder,and about 40-90%, more typically 50-70% by weight, of an aqueouscarrier.

The present composition suitably comprises about 5 to 98 percent,preferably 20 to 90%, suitably 40 to 80%, based on the weight of thebinder, of the specified graft polymer.

The graft copolymer contains about 2-98%, preferably 5-40%, and mostpreferably 15-40% by weight of macromonomer and correspondingly about98-2%, preferably 60-95%, most preferably 60-85% by weight of backbonepolymer. The graft copolymer has a weight average molecular weight ofabout at least 3,000, preferably 20,000 to 500,000, most preferably20,000 to 300,000. The side chains of the graft copolymer are formedfrom relatively water soluble macromonomers that have a weight averagemolecular weight of about 500-30,000 and preferably 3,000-10,000 andcontain about 10-100% by weight and preferably 20-40% by weight, basedon the weight of the macromonomer, of polymerized ethylenicallyunsaturated acid or amine monomers which are then at least partiallyneutralized. These side chains are relatively hydrophilic and keep thegraft polymer well dispersed in the resulting coating composition.

The backbone of the graft copolymer is hydrophobic relative to the sidechains and contain polymerized ethylenically unsaturated acid or aminemonomers or salts thereof. The backbone may contain polymerized monomerswhich are preferably acrylates or styrene, but which can contain 50% ofmethacrylates. Such monomers may comprise alkyl methacrylates andacrylates, cycloaliphatic methacrylates and acrylates and arylmethacrylates and acrylates as are listed hereinafter. It may contain upto 50% by weight, based on the weight of the graft copolymer, ofpolymerized ethylenically unsaturated non-hydrophobic monomers which maycontain reactive functional groups other than acid or amine. Examples ofsuch monomers are hydroxy ethyl acrylate, hydroxy ethyl methacrylate,acrylamide, nitro phenol acrylate, nitro phenol methacrylate,phthalimido methyl acrylate, and phthalimido methacrylate. Other vinylmonomers can be incorporated into the backbone, e.g., ethylenicallyunsaturated sulfonic, sulfinic, phosphoric or phosphonic acid and estersthereof also can be used such as styrene sulfonic acid, acrylamidomethyl propane sulfonic acid, vinyl phosphonic acid and its esters andthe like.

In one embodiment, the waterborne acrylic graft copolymers contain 0-60or more preferably 10-40 parts by weight of hydroxy functional acrylicmonomers, e.g., 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate,2-hydroxypropyl acrylate, 2-hydroxypropyl methacrylate, 2-hydroxbutylacrylate, and 4-hydroxybutyl acrylate. All or most of these may bepresent in the side chains and may serve as crosslinking sites.

As indicated earlier, the graft polymer comprises macromonomeric sidechains attached to a polymeric backbone. Each macromonomer ideallycontains a single terminal ethylenically unsaturated group which ispolymerized into the backbone of the graft copolymer and typicallycontains polymerized monomers of methacrylic acid, its esters (includingacid and amino esters), nitriles, amides or mixtures of these monomers.

The above-mentioned acids or amines also can be used in the backbone ofthe graft copolymer, but usually in a lesser amount by weight than inthe macromonomeric arms, in order to maintain the water-insolubility ofthe backbone. In such a case, however, the selection of acid or amine inthe backbone should be consistent with the use of either acid or aminein the macromonomers.

In addition to the acid or amine, up to 90% by weight, based on theweight of the macromonomer, of other polymerized ethylenicallyunsaturated monomers can be present in the macromonomer, for example,but not limited to acrylic and methacrylic acid esters of straight-chainor branched monoalcohols of 1 to 20 carbon atoms. The majority of these,greater than 50%, preferably 60-80% of the macromonomer, should bemethacrylates, for example, alkyl methacrylates having 1-12 carbons inthe alkyl group can be used such as methyl methacrylate, ethylmethacrylate, propyl methacrylate, isopropyl methacrylate, butylmethacrylate, pentyl methacrylate, hexyl methacrylate, 2-ethylmethacrylate, nonyl methacrylate, lauryl methacrylate and the like canbe used. Cycloaliphatic methacrylates can be used such astrimethylcyclohexyl methacrylate, t-butyl cyclohexyl methacrylate,isobornyl methacrylate, 2-ethylhexyl methacrylate, and the like. Arylmethacrylates such as benzyl methacrylate also can be used.

Ethylenically unsaturated monomers containing hydroxy functionalityinclude hydroxy alkyl acrylates and hydroxy alkyl methacrylates, whereinthe alkyl has 1 to 12 carbon atoms. Suitable monomers include hydroxyethyl acrylate, hydroxy propyl acrylate, hydroxy isopropyl acrylate,hydroxy butyl acrylate, hydroxy ethyl methacrylate, hydroxy propylmethacrylate, hydroxy isopropyl methacrylate, hydroxy butylmethacrylate, and the like, and mixtures thereof. Reactive functionalitymay also be obtained from monomer precursors, for example, the epoxygroup of a glycidyl methacrylate unit in a polymer. Such an epoxy groupmay be converted, in a post polymerization reaction with water or asmall amount of acid, to a hydroxy group, or with ammonia and/or aprimary amine to give a hydroxy amine.

Suitable other olefinically unsaturated comonomers include: acrylamideand methacrylamide and derivatives as alkoxy methyl (meth) acrylamidemonomers, such as methacrylamide, N-isobutoxymethyl methacrylamide, andN-methylol methacrylamide; maleic, itaconic and maleic anhydride and itshalf and diesters; vinyl aromatics such as styrene and vinyltoluene;polyethylene glycol monoacrylates and monomethacrylates; aminofunctional(meth) acrylates as, e.g., diethylaminoethylmethacrylate andt-butylaminoethylmethacrylate; glycidyl functional (meth) acrylates asglycidylmethacrylate.

Other functional monomers as acrylonitrile, acrolein, allylmethacrylate, aceto acetoxyethyl methacrylate, methylacrylamidoglycolate methylether, ethylene ureaethyl methacrylate,2-acrylamide-2 methyl propanesulfonic acid, trialkoxy silyl propylmethcrylate, reaction products of mono epoxyesters or monoepoxy etherswith alpha-beta unsaturated acids and reaction products of glycidyl(meth) acrylate with mono functional acids up to 22 carbon atoms.

The above monomers also can be used in the backbone of the graftcopolymer.

The graft polymer may be prepared by polymerizing ethylenicallyunsaturated monomers in the presence of macromonomers each having aterminal ethylenic unsaturation for grafting. The resulting graftpolymer can be envisioned as being composed of a backbone having aplurality of macromonomer "arms" attached thereto. In the presentcomposition, both the macromonomer arms and the backbone may havereactive functionalities capable of reacting with a crosslinkingcompound or polymer, although it is optional to have such reactivefunctionalities only on the macromonomers. It is to be understood thatthe macromonomers referred to as having carboxylic functionality may bepart of a mixture of macromonomers of which a portion do not have anycarboxylic functionality or variable amounts of carboxylicfunctionality.

To ensure that the resulting macromonomer only has one terminalethylenically unsaturated group which will polymerize with the backbonemonomers to form the graft copolymer, the macromonomer is polymerized byusing a catalytic chain transfer agent. Typically, in the first step ofthe process for preparing the macromonomer, the monomers are blendedwith an inert organic solvent which is water miscible or waterdispersible and a cobalt chain transfer agent and heated usually to thereflux temperature of the reaction mixture. In subsequent stepsadditional monomers and cobalt catalyst and conventional polymerizationcatalyst are added and polymerization is continued until a macromonomeris formed of the desired molecular weight.

Preferred cobalt chain transfer agents or catalysts are described inU.S. Pat. No. 4,680,352 to Janowicz et al, U.S. Pat. No. 4,722,984 toJanowicz and WO 87/03605. Most preferred are pentacyanocobaltate (II orIII), diaquabis(borondifluorodimethyl-glyoximato) cobaltate (II or III)and diaquabis(borondifluorophenylglyoximato) cobaltate (II or III),ethylenically unsaturated sulfonic, sulfinic, phosphoric or phosphonicacid and esters thereof also can be used such as styrene sulfonic acid,acrylamido methyl propane sulfonic acid, vinyl phosphonic acid and itsesters and the like. Typically these chain transfer agents are used atconcentrations of about 5-1000 ppm based on the monomers used.

The macromonomer is preferably formed in a solvent or solvent blendusing a free radical initiator and a Co (II or III) chelate chaintransfer agent, although it can be formed in aqueous solution oremulsion when using, for example,diaquabis(borondifluorodimethyl-glyoximato) cobaltate (II or III).

Azoinitiators (0.5-5% weight on monomer) can be used in the synthesis ofthe macromonomers in the presence of 2-5,000 ppm (on total monomer) orCo (II) chelate in the temperature range between 70-180° C., morepreferably azo type initiators as, e.g., 2,2'-azobis (2,4dimethylpentanenitrile), 2,2'-azobis (2-methylpropanenitrile),2,2'-azobis (2-methylbutanenitrile), 1,1'-azo (cyclohexane carbonitrile)and 4,4'-azobis (4-cyanopentanoic) acid.

Typical solvents that can be used to form the macromonomer copolymer arearomatics, aliphatics, ketones such as methyl ethyl ketone, isobutylketone, ethyl amyl ketone, acetone, alcohols such as methanol, ethanoln-butanol isopropanol esters such as ethyl acetate, glycols such asethylene glycol propylene glycol ethers such as tetrahydrofuran,ethylene glycol mono butyl ether and the like, and as mentioned above,water and mixtures thereof with water miscible solvents.

After the macromonomer is formed as described above, solvent isoptionally stripped off, the macromonomer neutralized, and the backbonemonomers added to the macromonomer along with polymerization catalyst.As neutralizing agents for acids can be used inorganic bases includeammonium hydroxide, sodium hydroxide, or potassium hydroxide. Typicalamines that can be used as neutralizing agents include amino methylpropanol, amino ethyl propanol, dimethyl ethanol amine, triethylamine,dimethylethanolamine, dimethylaminomethylpropanol andaminomethylpropanol and the like. One preferred amine is amino methylpropanol and the preferred inorganic base is ammonium hydroxide.

As neutalizing agents for amines, organic or inorganic acids can beused, for example, acetic acid, formic acid, lactic acid, hydrochloricacid, sulfuric acid, and the like.

As indicated above, the graft copolymer is formed directly into water,wherein the macromonomer is first neutralized and dispersed or dissolvedinto water. The graft copolymer is formed by copolymerizing the rest ofthe monomer blend in the presence of the macromonomer water solution ordispersion. This procedure has the advantage that less cosolvent shouldbe used in the overall process and solvent stripping can be eliminated.Another advantage is that higher molecular weight graft polymers can beobtained than in solvent polymerization.

Mixtures of suitably compatible macromonomers can be used as long as allare either anionic or cationic in water.

Any of the aforementioned azo type catalysts can be used as can othersuitable catalysts such as peroxides and hydroperoxides. Typical of suchcatalysts are di-tertiarybutyl peroxide, di-cumylperoxide, tertiaryamylperoxide, cumenehydroperoxide, di(n-propyl) peroxydicarbonate, peresterssuch as amyl peroxyacetate and the like. Polymerization is continuedusually at the reflux temperature of the reaction mixture until a graftcopolymer is formed of the desired molecular weight.

Water-soluble free radical initiators can be used, suitably in thetemperature range of 20-98° C., e.g., peroxides such as ammoniumpersulfate, or redoxinitiators such as t-butylhydroperoxide/ascorbicacid. On copolymerizing the monomers with the macromonomer optionallychain transfer agents other than the cobalt chelates can be used as,e.g., mercaptans: mercaptoethanol, t-dodecylmercaptan,N-dodecylmercaptan.

In the synthesis of the graft copolymer small amounts of difunctionalalpha-beta unsaturated compounds can be used as, e.g., ethyleneglycoldimethacrylate or hexanedioldiacrylate. This can result in crosslinkedparticles.

The overall graft copolymer water borne dispersion should becharacterized by an acid or amine value of from 10 to about 150 (mgKOH/g resin solids), more preferably from 15 to about 70 and still morepreferably from 15 to about 35, and an hydroxyl number of about 0 toabout 250 (mg KOH/g resin solids), more preferably from 40 to 150.

The degree of neutralization of the dispersion can be from 10 to 150% ofthe total amount of acid or amine groups, preferably from 80-105%. Thefinal pH of the dispersion can accordingly be about 4-10, preferably7-10 for an anionic system and 4-7 for a cationic system. Anionic,cationic or non-ionic surfactants can be used, but preferably not sincethey might hurt humidity resistance afterwards. As indicated above, nothaving to use a surfactant is one of the significant advantages of thepresent invention.

The afore-described binder systems are utilized to produce waterbornecoatings by blending with other suitable components in accordance withnormal paint formulation techniques.

The graft copolymers of the present invention are useful as film formingvehicles in the preparation of waterborne coatings compositions such as,for example, clearcoat or basecoat compositions useful in automotiveapplications. The resultant coating compositions have low volatileorganic content, preferably to a maximum of 3.50 pounds/gallon.

In preparing the coating compositions of the present invention, thegraft copolymer is combined with a crosslinking agent in the amount of 2to 50 percent by weight of binder, preferably 10 to 40 percent by weightof binder.

If the binder is used in a formulation that is cured with a curing agentcontaining N-methylol and/or N-methylol ether groups, the curing agentshould be dispersed in the water based graft copolymer dispersion toform a stable overall dispersion. Examples of such curing agents areamino resins obtained by reacting an aldehyde, such as formaldehyde,with a compound containing amino group such as melamine, urea andbenzoguanamine and total or partial etherification of the N-methylolgroup with an alcohol such as, e.g., methanol, n-butanol, isobutanol.

To form a composition which will crosslink under elevated bakingtemperatures of about 60-180° C. for abut 5-60 minutes, about 10 to 60%,preferably 10 to 25% by weight, based on the weight of the binder, of awater-soluble water dispersible alkylated melamine formaldehydecrosslinking agent having 1-4 carbon atoms on the alkylated group ispreferred.

These crosslinking agents are generally partially alkylated melamineformaldehyde compounds and may be monomeric or polymeric and ifpolymeric have a degree of polymerization of about 1-3. Typical alcoholsused to alkylate these resins are methanol, ethanol propanol, butanol,isobutanol and the like. preferred alkylated melamine crosslinkingagents that are commercially available include Cymel™ 373, 385, 1161,350, or 1168 (Monsanto) or Resimine™ 714, Resimine™ 730 and 731,Resimine™ 735 and 745 (Cyanamid).

Coating compositions of this invention containing a melaminecrosslinking agent can contain about 0.1 to 1.0%, based on the weight ofa binder, of a strong acid catalyst or a salt thereof to lower curingtemperatures and time. Paratoluene sulfonic acid is a preferred catalystor its ammonium salt. Other catalysts that can be used are dodecylbenzene sulfonic acid, phosphoric acid and amine or ammonium salts ofthese acids.

If the binder is used in a formulation that is cured with apolyisocyanate, a water dispersible polyisocyanate is added to thewaterborne graft copolymer dispersion prior to application.

The overall dispersion is not stable in this case and should be usedwithin a certain time period. Examples of water dispersiblepolyisocyanates include biuret and cyclotrimers of hexamethylenediisocyanate, isophorone diisocyanate and tetramethyl xylylenediisocyanate. These isocyanates may be modified to such an extent thatthey contain ionic groups to ease dispersion into water.

Typically, a cure promoting catalyst is utilized in conjunction with theisocyanate crosslinking or curing agent. Preferred catalysts areorganometallics, suitably dibutyl tin dilaurate, dibutyl tindi-2-ethylhexoate, zinc octoate, zinc napthenate, vanadium acetylacetonate, or zirconium acetyl acetonate, in an effective curing amount,typically from about 0.1 to 2% by weight of binder. Such catalysts areoptional, for example, elevated temperature and/or time may suffice tocure the composition.

Typical isocyanate crosslinking agents which may be used for curing thecomposition include both compounds and polymers, blocked or unblocked.Examples of suitable polyisocyanates include monomeric polyisocyanatessuch as toluene diisocyanate and4,4'-methylene-bis(cyclohexylisocyanate), isophorone diisocyanate andNCO-prepolymers such as the reaction products of monomericpolyisocyanate such as those mentioned above with polyester or polyetherpolyols. Particularly useful isocyanates are isophorone diisocyanate andthe biuret-form 1,6-hexamethylene diisocyanate commercially availablefrom Bayer as "Desmodur" N or the like. Other crosslinking agentsinclude 4,4'-biphenylene diisocyanate, tetramethyl diisocyanate,ethylethylene diisocyanate, 1,3-cyclopentylene diisocyanate,1,3-phenylene diisocyanate, 1,5-naphthalene diisocyanate,bis(4-isocyanatocyclohexyl)methane, and the like.

Trifunctional isocyanates may be used, for example, triphenylmethanetriisocyanate, 1,3,5-benzene triisocyanate, 2,4,6-toluene triisocyanate,an adduct of trimethylol and tetramethyl xylene diisocyanate sold underthe tradename "Cythane 3160," "Desmodur" N 3390 which is the trimer ofhexamethylene diisocyanate, and the like. Optionally, one can use apolyisocyanate acrylic copolymer derived from isocyanatoethylmethacrylate (commercially available as TMI) and the like, as forexample disclosed in U.S. Pat. No. 4,965,317 (col. 5).

As indicated above, the polyisocyanate may optionally be blocked.Examples of suitable blocking agents are those materials which wouldunblock at elevated temperatures, for example, lower aliphatic alcoholssuch as methanol, oximes such as methylethyl ketone oxime, and lactamssuch as epsiloncaprolactam. Blocked isocyanates can be used to formstable one-package systems. Polyfunctional isocyanates with freeisocyanate groups can be used to form two-package room temperaturecurable systems. In these systems, the product and isocyanate curingagent are mixed just prior to their application.

Other film-forming polymers, preferably 0 to 55 percent by weight (andconcomitantly 45 to 100% by weight of the graft copolymer), based on theweight of the binder, may also be used in conjunction with the graftcopolymer. Other film forming polymers may be linear or branched and mayinclude acrylics, acrylourethanes, polyesters, polyester urethanes,polyethers, and polyether urethanes that are compatible with the graftpolymer.

An organic cosolvent is also typically utilized in the presentcomposition, preferably in minimal amounts, less than 20% by weight ofcarrier, to facilitate formulation and application of the coatingcompositions of the present invention. An organic solvent is utilizedwhich is compatible with the components of the composition.

The amounts of graft copolymer, curing agent, and catalyst will ofcourse, vary widely depending upon many factors, among them the specificcomponents of the composition and the intended use of the composition.

In addition, a composition according to the present invention maycontain a variety of other optional ingredients, including pigments,pearlescent flakes, fillers, plasticizers, antioxidants, surfactants andflow control agents.

To improve weatherability of a finish produced by the present coatingcomposition, an ultraviolet light stabilizer or a combination ofultraviolet light stabilizers can be added in the amount of about 0.1-5%by weight, based on the weight of the binder. Such stabilizers includeultraviolet light absorbers, screeners, quenchers, and specific hinderedamine light stabilizers. Also, an anitoxidant can be added, in the about0.1-5% by weight, based on the weight of the binder.

Typical ultraviolet light stabilizers that are useful includebenzophenones, triazoles, triazines, benzoates, hindered amines andmixtures thereof. Specific examples of ultraviolet stabilizers aredisclosed in U.S. Pat. No. 4,591,533.

The composition may also include conventional formulation additives suchas flow control agents, for example, Resiflow® S (polybutylacrylate),BYK 320 and 325 (high molecular weight polyacrylates); rheology controlagents, such as fumed silica, microgels, and non-aqueous dispersionpolymers; water scavengers such as tetrasilicate, trimethylorthoformate, triethyl orthoformate, and the like.

When the present composition is used as a clearcoat (topcoat) over apigmented colorcoat (basecoat) to provide a colorcoat/clearcoat finish,small amounts of pigment can be added to the clear coat to providespecial color or aesthetic effects such as tinting.

The present composition can be pigmented and used as the colorcoat,monocoat, primer, or primer surfacer. The composition has excellentadhesion to a variety of metallic or non-metallic substrates, such aspreviously painted substrates, cold rolled steel, phosphatized steel,and steel coated with conventional primers by electrodeposition. Thepresent composition can be used to coat plastic substrates such aspolyester reinforced fiberglass, reaction injection-molded urethanes andpartially crystalline polyamides.

When the present coating composition is used as a basecoat, typicalpigments that can be added to the composition include the following:metallic oxides such as titanium dioxide, zinc oxide, iron oxides ofvarious colors, carbon black, filler pigments such as talc, china clay,barytes, carbonates, silicates and a wide variety of organic coloredpigments such as quinacridones, copper phthalocyanines, perylenes, azopigments, indanthrone blues, carbazoles such as carbazole violet,isoindolinones, isoindolones, thioindigo reds, benzimidazolinones,metallic flake pigments such as aluminum flake and the like.

The pigments can be introduced into the coating composition by firstforming a mill base or pigment dispersion with any of the aforementionedpolymers used in the coating composition or with another compatiblepolymer or dispersant by conventional techniques, such as high speedmixing, sand grinding, ball milling, attritor grinding or two rollmilling. The mill base is then blended with the other constituents usedin the coating composition. to obtain the present coating compositions.

The coating composition can be applied by conventional techniques suchas spraying, electrostatic spraying, dipping, brushing, flowcoating andthe like. The preferred techniques are spraying and electrostaticspraying. The present composition may be used as an ambient cure,especially for refinish, or at elevated temperature. In OEMapplications, the composition is typically baked at 100-150° C. forabout 15-30 minutes to form a coating about 0.1-3.0 mils thick. When thecomposition is used as a clearcoat, it is applied over the colorcoatwhich may be dried to a tack-free state and cured or preferably flashdried for a short period before the clearcoat is applied. Thecolorcoat/clearcoat finish is then baked as mentioned above to provide adried and cured finish.

It is customary to apply a clear topcoat over a basecoat by means of a"wet-on-wet" application, i.e., the topcoat is applied to the basecoatwithout curing or completely drying the basecoat. The coated substrateis then heated for a predetermined time period to allow simultaneouscuring of the base and clear coats.

The following examples illustrate the invention. All parts andpercentages are on a weight basis unless otherwise indicated. Allmolecular weights disclosed herein are determined by gel permeationchromatography using a polystyrene standard.

EXAMPLES 1-2

This example illustrates the use of a Co (II) chelate in the synthesisof the following macromonomers. The chelate is BF₂ bridged Co (II)(1,2-diphenyl-1,2-dioxoiminoethane)₂ (H₂ O)₂ chelate, as described inexample 44B of EP 0199436. Mixture 1 (of Table 1 below) was heated atreflux (±80° C.) in a reaction vessel that was kept under nitrogen.Mixture 2 was added over 4 hours. Simultaneously with the addition ofmixture 2, mixture 3 was added over 90 min. followed immediately bymixture 4. Mixture 5 was added, for rinsing, followed by a 5 min. hold.Afterwards, mixture 6 was added over 30 min. followed by another rinsingstep and held for 60 min. During the total process, the temperature waskept at reflux. As evident from Table 1, various combinations ofmonomers were used in Examples 1 to

                  TABLE 1    ______________________________________                   Example 1                          Example 2    ______________________________________    Mixture 1    Methyl ethyl ketone                     20       20    Mixture 2    Methyl           30       26    methacrylate    2-Hydroxyethyl            14    methacrylate    Methacrylic acid 20       10    Methyl ethyl ketone                     6        6    Mixture 3    Methyl ethyl ketone                     4        4    Co II chelate    0.006    0.006    Vazo\67 initiator                     0.35     0.35    Mixture 4    Methyl ethyl ketone                     10       10    Co II chelate    0.003    0.003    Vazo\52 initiator                     0.3      0.3    Mixture 5    Methyl ethyl ketone                     1.23     1.23    Mixture 6    Vazo\52 initiator                     0.1      0.1    Methyl ethyl ketone                     1.9      1.9    Methyl ethyl ketone                     1        1    (Rinse)    Final Thinning    Methyl ethyl ketone                     5.111    5.111    TOTAL            100      100    TEST RESULTS    SOLIDS           51.8     50.2    VISCOSITY        Z3       I - 14    (Gardner-Holdt)    ACID VALUE       252      143    MN               2306     1500    MW               4800     3000    ______________________________________

EXAMPLE 3

This example again illustrates the use of a Co (II) chelate in thesynthesis of the following macromonomers which comprise carboxylic-acidand hydroxy functionality. The chelate is the same as in the aboveExamples 1-2, as described in EP 0199436. A glass reactor with twoinlets, one for the monomer feed and one for the initiator feed wasemployed. The reaction mixture was kept at reflux temperature throughoutthe process, while the following components were introduced into thereactor as explained below.

    ______________________________________                      Parts By Weight    ______________________________________    Part 1    Isopropyl alcohol   25    Itaconic acid       18    Part 2    Methyl methacrylate 42    Vazo\67 initiator                        0.3    Methyl ethyl ketone 6.68    Co II chelate       0.02    Part 3    Methyl ethyl ketone 1    Part 4    t-Butylperpivalate  0.1    (Triganox ™ 25 C-75 from AKZO)    Isopropyl alcohol   4.9    Part 5    Isopropyl alcohol   2    TOTAL               100    ______________________________________

Part 1 was heated to reflux, under nitrogen, until dissolved. Part 2 wasthen added over 2 hours. Part 3 was used for rinsing. The mixture wasthen held at reflux for 1 hour. Part 4 was fed over 1 hour. Part 5 wasused for rinsing, and then the reaction mixture was held at reflux forone hour. The reaction product was characterized, including AN (acidnumber), MN (number average molecular weight , and MW (weight averagemolecular weight), as follows:

    ______________________________________           Solids (%)     60.6           Viscosity      >Z6           AN             229           MN             1100           MW =           3600    ______________________________________

EXAMPLE 4

This example illustrates the use of a Co (II) chelate in the synthesisof an acid functional macromonomer, which is then dissolved in water.The equatorial ligands of this chelate are BF₂ bridged2,3-dioxyimiomethane groups. as described in EP 0199436. The followingcomponents were reacted in a glass reactor as explained below.

    ______________________________________                  Parts by Weight    ______________________________________    Part 1    N-Butanol       20.0    Co II chelate   0.02    Part 2    n-Butyl methacrylate                    34.4    Methacrylic acid                    5.6    Vazo ® 67 initiator                    0.2    n-Butylglycolether                    3.3    Part 3    n-Butylglycolether                    1.0    Part 4    Vazo ® 67 initiator                    0.2    n-Butylglycolether                    2.8    Part 5    n-Butylglycolether                    0.5    Part 6    Dimethylethanolamine                    5.8    Deionized water 0.2    Part 7    Deionized water 126    TOTAL           200    ______________________________________

Part 1 was heated, under nitrogen, at reflux. Part 2 was then added over3 hours. Part 3 was used for rinsing and the mixture was held at refluxfor 10 minutes. Part 4 was added over 1 hour and Part 5 was used forrinsing. The mixture was then held at reflux for 10 minutes and cooledto 80° C. Part 6 was then added and mixed for 10 minutes, followed byPart 7 (deionized water) for rinsing. The product exhibited thefollowing characteristics:

    ______________________________________           Solids         19.4           Viscosity      E           pH             8.6           MN             3200           MW             6100.    ______________________________________

Comparative Example 5

This example illustrates the use of a sulfur chain transfer agent in thesynthesis of an acid functional polymer. In particular, this exampleillustrates the preparation of an n-butyl methacrylate/methacrylic acid(96/14) copolymer with a sulfur chain transfer agent.

    ______________________________________                  Parts by Weight    ______________________________________    Part 1    n-Butanol       20.0    Part 2    n-Butyl methacrylate                    34.4    Methacrylic acid                    5.6    Vazo ® 67 initiator                    0.2    n-Butylglycolether                    1.3    N-dodecylmercaptan                    2.0    Part 3    n-Butylglycolether                    1.0    Part 4    Vazo ® 67 initiator                    0.2    n-Butylglycolether                    2.6    Part 5    n-Butylglycolether                    0.5    Part 6    Dimethylethanolamine                    5.8    Deionized water 0.3    Part 7    Deionized water 126    TOTAL           200    ______________________________________

Part 1 (solvent) was heated to reflux. Part 2 (including monomermixture) was added over 3 hours at reflux, and Part 3 was used forrinsing. The mixture was held at reflux for 10 minutes and then Part 4(additional initiator) was added over 1 hour. Part 5 was used forrinsing, and the mixture was again held at reflux for 10 minutes,followed by cooling to 80° C. Part 6 (including amine and deionizedwater) was then added and mixed for 10 minutes, followed by rinsing withthe additional deionized water of Part 7. The product exhibited thefollowing characteristics.

    ______________________________________    Solids          20.7    Viscosity       Q    pH              8.9    MN =            3400 (peak molecular weight)    MW =            6500    ______________________________________

EXAMPLE 6

This example illustrates the preparation of a graft acrylic copolymerdispersion. In particular, this example illustrates the preparation of agraft polymer comprising 70% by weight methyl methacrylate/n-butylacrylate (in the ratio of 20/80) reacted with 30% macromonomer(abbreviated "macro") of n-butyl methacrylate/methacrylic acid (in theweight ratio of 86/14). The following components were reacted asexplained below.

    ______________________________________                    Parts by Weight    ______________________________________    Part 1    Macro of Example 5                      9    Deionized water   10    Part 2    Methyl methacrylate                      4.2    n-Butyl acrylate  16.8    Vazo ® 67 initiator                      0.1    n-Butylglycolether                      0.9    Macro of Example 5                      36    Deionized water   22    Part 3    n-Butylglycolether                      1    ______________________________________

Part 1 was heated to 90-95° C. Part 2 was added simultaneously over 4hours, after which Part 3 was used for rinsing. The mixture was held atreflux for 1 hour. The product was a stable dispersion, with no settlingon storage, and exhibited the following properties.

    ______________________________________    Solids         29.1%    MN             8800 (peak molecular weight)    MW             93800.    ______________________________________

Comparative Example 7

For comparison to Example 6, this example illustrates the preparation ofan acylic copolymer, but in which the macromonomer used in Example 4 wasreplaced with the macromonomer of Example 5 which has approximately thesame molecular weight and monomer composition. This acrylic copolymershows a bimodal distribution which proves that the macromonomer ofExample 5 is not copolymerized to provide stabilization of the overallcomposition. The dispersion is therefore not stable and settles out.

EXAMPLE 8

This example illustrates the preparation of a graft acrylic copolymerconsisting by weight 95% backbone made from styrene/n-butylacrylate/2-hydroxypropyl methacrylate (in the weight ratio of 27/40/28)and 5% macromonomer (from Example 1) made from methylmethacrylate/methacrylic acid (in the weight ratio 3/2). This graftcopolymer was formed in a water dispersion using the followingcomponents:

    ______________________________________    Part 1    Deionized water     24.85    Macro Example 1     4.5    Dimethylethanolamine                        0.9    Part 2A (monomer solution)    Styrene             12.15    n-Butyl acrylate    18.0    Hydroxypropyl methacrylate                        12.60    Part 2B (azo solution)    Acid-Azo (4,4'-azobis-(4-cyano                        2.0    pentanecarboxylic acid)    Dimethylethanolamine                        1.2    Deionized water     18.8    Part 3    Deionized water     2.0    Part 4    t-Butylperpivalate  0.1    Methyl ethyl ketone 0.7    Part 5    n-Butanol           0.2    Part 6    Deionized water     2.0                        100.0    ______________________________________

Part 1 was heated to 95° C., plus or minus 2 degrees, and adjusted to apH of 7.5-7.8. Part 2A (monomers) and 2B (azo solution) were addedsimultaneously over 4 hours at 95° C., ±2° C. Part 3 (deionized water)was used for rinsing and the mixture was held for 30 min at reflux. Part4 was then added over 60 min and the reactor inlet rinsed with Part 5.The mixture was then again held at 95±2° C. for 30 min. and finallyrinsed with Part 6 (water). The reaction product was characterized asfollows:

    ______________________________________    Solids (percent) =   50.5    Viscosity =          500 cps    pH =                 8.1    MN =                 39000    MW =                 117200    ______________________________________

EXAMPLE 9

This example illustrates the preparation of a graft acrylic copolymerconsisting by weight 90% backbone made from styrene/n-butylacrylate/2-hydroxypropyl methacrylate (in the weight ratio of 47/38/25)and 10% macromonomer (from Example 2) made from methylmethacrylate/hydroxyethyl methacrylate or EHMA/methacrylic acid (in theweight ratio 5.2/2.8/2). This graft copolymer was formed in a waterdispersion using the following components:

    ______________________________________    Part 1    Deionized water     23.85    Macro Example 2     9.0    Dimethylethanolamine                        0.9    Part 2A (monomer solution)    Styrene             12.15    n-Butyl acrylate    17.10    Hydroxypropyl methacrylate                        11.25    Part 2B (azo solution)    Acid-Azo            2.0    Dimethylethanolamine                        1.2    Deionized water     17.8    Part 3    Deionized water     2.0    Part 4    t-Butylperpivalate  0.1    Methylethyl ketone  0.7    Part 5    n-Butylglycolether  0.2    Part 6    Deionized water     2.0                        100.0    ______________________________________

Part 1 was heated to 95° C., plus or minus 2 degrees, and adjusted to apH of 7.5-7.8. Part 2A (monomers) and 2B (azo solution) were addedsimultaneously over 4 hours at 95° C., ±2° C. Part 3 (deionized water)was used for rinsing and the mixture was held for 30 min at reflux. Part4 was then added over 60 min and the reactor inlet rinsed with Part 5.The mixture was then again held at 95±2° C. for 30 min. and finallyrinsed with Part 6 (water). The reaction product was characterized asfollows:

    ______________________________________           Solids =      47.7           Visc =        1500 cps           pH =          8.5           MN =          20500           MW =          79400    ______________________________________

EXAMPLE 10

This example illustrates the preparation of a graft acrylic copolymerconsisting by weight of 90% backbone made from styrene/n-butylacrylate/2-hydroxypropyl methacrylate (in the weight ration of 22/40/28)and 10% macromonomer (from Example 1) made of methylmethacrylate/methacrylic acid (in the weight ratio of 6/4). This graftcopolymer was formed in a water dispersion using the followingcomponents:

    ______________________________________                     Parts by Weight    ______________________________________    Part 1    Deionized water    22.60    Macro Example 1    9.0    Dimethylethanolamine                       1.8    Part 2A    Styrene            9.9    n-Butyl acrylate   18.0    2-Hydroxypropyl methacrylate                       12.6    Part 2B    Acid-Azo           2.0    Dimethylethanolamine                       1.2    Deionized water    17.9    Part 3    Deionized water    2    Part 4    t-Butylperpivalate 0.1    n-Butylglycolether 0.7    Part 5    n-Butylglycolether 0.2    Part 6    Deionized water    2.0                       100.0    ______________________________________

Part 1 was heated to reflux at 95±2° C. and the pH adjusted to 7.5-7.8.Part 2A (monomers) and Part 2B (azo solution) was added simultaneouslyover 4 hours at 95° C.±2 C. Then the inlet was rinsed with Part 3(deionized water) and the mixture held at reflux for 30 min. Part 4 wasadded over 60 min. and rinsed with part 5 solvent. Finally, deionizedwater (Part 6) was added. The reaction product was characterized asfollows:

    ______________________________________            Solids       49.9            Visc         1500 cps            pH           8.2            MN           22900            MW           78400    ______________________________________

EXAMPLE 11

This example illustrates the preparation of a graft acrylic copolymerconsisting by weight of 80% backbone made from styrene/n-butylacrylate/2-hydroxypropyl methacrylate (in the weight ration of22/136/22) and 20% macromonomer (from Example 2) made of methylmethacrylate/hydroxyethyl methacrylate/methacrylic acid (in the weightratio of 10.4/5.6/4). This graft copolymer was formed in a waterdispersion using the following components:

    ______________________________________                     Parts by Weight    ______________________________________    Part 1    Deionized water    18.10    Macro Example 2    18.0    Dimethylethanolamine                       1.8    Part 2A    Styrene            9.9    n-Butyl acrylate   16.2    2-Hydroxypropyl methacrylate                       9.9    Part 2B    Acid-Azo           2.0    Dimethylethanolamine                       1.2    Deionized water    17.9    Part 3    Deionized water    2.0    Part 4    t-Butylperpivalate 0.1    n-Butylglycolether 0.7    Part 5    n-Butylglycolether 0.2    Part 6    Deionized water    2.0                       100.0    ______________________________________

Part 1 was heated to reflux at 95±2° C. and the pH adjusted to 7.5-7.8.Part 2A (monomers) and Part 2B (azo solution) was added simultaneouslyover 4 hours at 95° C.±2 C. Then the inlet was rinsed with Part 3(deionized water) and the mixture held at reflux for 30 min. Part 4 wasadded over 60 min. and rinsed with part 5 solvent. Finally, deionizedwater (Part 6) was added. The reaction product was characterized asfollows:

    ______________________________________           Solids       52.1 percent           Visc         18000 cps           pH           8.1           MN           18700           MW           52500    ______________________________________

EXAMPLE 12

This example illustrates another graft copolymer comprising 92.5%backbone made from styrene/n-butyl acrylate/2-hydroxybutyl acrylate (inthe weight ratio of 35/30/27.5) and 7% macromonomer (from Example 1)made from methyl methacrylate/methacrylic acid (in the weight ration of4.5/3). The graft copolymer was formed in a water dispersion of themacromonomer. The graft copolymer was prepared in a glass reactor usingthe following components:

    ______________________________________                     Parts by Weight    ______________________________________    Part 1    Deionized water    24.30    Macro of Example 1 6.75    Dimethylethanolamine                       1.32    Part 2A    Styrene            15.75    n-Butyl acrylate   13.50    2-Hydroxybutyl acrylate                       12.38    Part 2B    Acid-AZO           1.0    Dimethylethanolamine                       0.65    Deionized water    20.05    Part 3    Deionized water    2.0    Part 4    Deionized water    2.3                       100.0    ______________________________________

The pH of Part 1 was adjusted to 7.5-7.8 and the mixture was heated toreflux at 90° C. Part 2A (including monomers) and Part 2B (azo solution)was added simultaneously over 4 hours at 90° C. Part 3 was used forrinsing and then the reactor contents were held at reflux for 60 min,followed by pH adjustment to 8.0. Deionized water (Part 4was added Thereaction product was characterized as follows:

    ______________________________________           Solids       52.5 percent           Visc         1050 cps           pH           8           MN           25900           MW           112900    ______________________________________

Comparative Example 13

As a comparison for Example 13, a copolymer was prepared in one step,using no macromonomer, from a monomer mixture comprising styrene/methylmethacrylate/n-butyl acrylate/2-hydroxybutyl acrylate/methacrylic acid(in the weight ratio of 35/4.5/30/27.5/3). The dispersion was notstable.

EXAMPLE 14

The same procedure as in example 12 was used except that the monomers inthe backbone were changed to styrene (16.875 parts), butyl acrylate(13.50 parts) and hydroxypropyl acrylate (11.25 parts) in the weightratio of 37.5/30/25. The resulting graft copolymer was characterized asfollows:

    ______________________________________    Solids         51.1 percent    Visc           490 cps    pH             8.1    MN             12000    MW             122400    Particle Size  109 nm (92%) and 195 nm (8%)    (Bimodal)    ______________________________________

EXAMPLE 15

This example illustrates the preparation of a graft copolymer comprising92.5% backbone made from styrene/n-butyl acrylate/2-hydroxypropylmethacrylate (in the weight ratio of 25/40/27.5) and 7.5% macromonomer(from Example 1) made from methyl methacrylate/methacrylic acid (in theweight ratio of 4.5/3). In this example, the azo solution used in theabove Example 13 was replaced with 0.2 parts ammoniumpersulfate (AP) in21.5 parts in deionized water. The resulting stable graft polymer wascharacterized as follows:

    ______________________________________           Solids         48.4%           Viscosity      77 cps           pH             8           MN             7200           MW             132.600           Particle Size  210 nm    ______________________________________

EXAMPLE 16

This example illustrates a graft copolymer according to the presentinvention comprising 94% backbone made from styrene/methylmethacrylate/n-butyl acrylate/methacrylamide/2-hydroxyethyl acrylate (inthe weight ratio of 27/14.5/46/4/2.5) and 6% macromonomer (fromExample 1) made from methyl methacrylate/methacrylic acid (in the weightratio of 3.6/2.4). This graft copolymer copolymerized after dispersionin water using ammonia to form a high molecular weight binder with bothhydroxy (2-hydroxyethyl acrylate) and amide (methacrylamide)functionalities. The following components were used in the preparation:

    ______________________________________    Part 1    Deionized water    31.0    Macro of Example 1 4.8    Ammonia            0.75    Part 2A (monomers)    Styrene            10.8    Methyl methacrylate                       5.8    n-Butyl acrylate   18.4    2-Hydroxyethyl acrylate                       1.0    Methyl ethyl ketone                       0.2    Part 2B (azo-amide)    Acid-azo solution  0.2    Ammonia            0.1    Deionized water    20.35    Methacrylamide     1.6    Part 3    Deionized water    2.0    Part 4    Deionized water    8.0    Acid-azo           0.1    Ammonia            0.05    Deionized water    3.85    Part 5    Deionized water    1.0                       105.0    ______________________________________

Part 1 was heated to 90° C. and the pH adjusted to from 7.0 to 7.75.Part 2A (monomers) and Part 2B (azo-amide solution) was simultaneouslyadded over 4 hours. Part 3 (water) was used for rinsing and the mixtureheld at reflux for 60 min, followed by cooling and pH adjustment to 8.0to 8.5. Part 4 was added over 60 min, followed by rinsing with water(Part 5). The product was characterized as follows:

    ______________________________________    Solids            36.6 percent    Viscosity         very low    pH                8.4    MW                too high to measure    ______________________________________

EXAMPLES 17-19

These example illustrate graft copolymers formed in a water dispersionof the macromonomer wherein part of the macromonomer dispersion is addedsimultaneously with the monomers for reaction. Each of three examples(17, 18, and 19) were prepared analogously except that the backbonemonomers varied, as follows:

    ______________________________________    Backbone Monomers of    Graft Copolymer                   Ex. 17     Ex. 18  Ex. 19    ______________________________________    Styrene        25         37.5    40    Butyl acrylate 40         30      30.5    Hydroxylpropylacrylate                   27.5    Hydroxyproplyacrylate     25    Hydroxyethylacrylate              22    ______________________________________

In each of the three examples, the graft copolymer comprised 92.5%backbone, composed as indicated above, and 7.5% macromonomer accordingto Example 1 made from methyl methacrylate and methacrylic acid in theweight ratio of 4.5 to

    ______________________________________    Part 1    Deionized water      24.3    Macro of Example 1   2.0    Dimethylethanolamine 0.39    Part 2A (azo-macro solution)    Macro of Example 1   4.75    4,4'-Azobis(4-cyanopentanoic) acid                         1.0    Dimethylethanolamine 0.93    Deionized water      21.0    Part 2B    Monomers (according to                         41.625    above ratio)    Part 3    Deionized water      2.0    Part 4    t-Butylperpivalate   1.0    Methyl ethyl ketone  0.7    Part 5    Methyl ethyl ketone  0.2    Part 6    Deionized water      1.0                         100.0    ______________________________________

Part 1 was adjusted to a pH of 7 to 7.5 and heated to 90+12° C. Part 2A(azo-macro solution) and the Part 2B (monomers) were addedsimultaneously over 4 hours at 90° C. Part 3 (deionized water) was usedto rinse and then the reaction product was held at reflux for 30 min.Part 4 was added over 60 minute, followed by rinsing with methyl ethylketone (Part 5), pH adjustment to about 7.5 and the addition of somedeionized water (Part 6). The reaction products were characterized asfollows:

    ______________________________________    Property  Example 17  Example 18 Example 19    ______________________________________    Solids (percent)              50          49         50.1    Viscosity (cps)              300         1400       290    pH        7.8         7.4        7.5    MN        13600       15600      not soluble    MW        96000       161,600    not soluble    Particle Size (nm)              325          69 nm (45%)                                      57 nm (57%)                          251 nm (55%)                                     185 nm (43%)    ______________________________________

EXAMPLES 20-23

These examples illustrate a one component waterborne paint formulationcured by baking. The following examples were formulated at anacrylic/melamine formaldehyde ratio of 75/25 using a methylated melamineformaldehyde binder Cymel™ 325 from Cyanamid.

    ______________________________________    Components     Ex. 20  Ex. 21   Ex. 22                                          Ex. 23    ______________________________________    Acrylic graft    Copolymer Example 8                   70    Copolymer Example 9    70.33    Copolymer Example 10            69.97    Copolymer Example 11                  69.03    Cymel ™ 325 crosslinker                   14.7    17.97    18.33 19.27    Byk ™ 346 (Byk Chemie)                   0.5     0.5      0.5   0.5    Surfynol ™ 104 A                   0.2     0.2      0.2   0.2    surfactant    (Air Products)    n-Butylglycolether                   3       3        3     4    Deionized water                   11.6    8        7.7   6                   100     100      100   100    ______________________________________

These clear coats were sprayed over a typical commercial waterbornebasecoat at 50 microns and baked for 30 min. at 120° C. (spray viscosityof 600 mPaS). The following test results were obtained.

    ______________________________________    Property     Ex. 20  Ex. 21    Ex. 22                                         Ex. 23    ______________________________________    Pendulum hardness                 177     125       156   154    Sulfuric acid                 6       4         7     6    resistance 10% (min.)    Sulfuric acid                 4       2         2     3    resistance 36% (min.)    Gloss        91.9    94.7      94.6  92.9    Stone chipping                 1       4         2     2    (1 best-5 worst)    Humidity     OK      OK        OK    OK    Xylene resistance                 3       <3        3     3    (minutes)    ______________________________________

EXAMPLES 24-28

These examples illustrate a two component waterborne paint compositionaccording to the present invention, which composition is formulated forair dry (low bake) curing. These examples were formulated using Basonat™PLR 8878X, which is a trifunctional isocyanate commercially availablefrom BASF and which is water dispersible. After mixing the Basonat™ PRL8878X crosslinker at an isocyanate/hydroxyl equivalent ratio of 1/1, theviscosity (cps), hardness (Persoz) and % NCO remaining (on a film of±30microns via IR analysis) was measured after 1 day and 14 days.

    ______________________________________    Component    Ex. 24  Ex. 25  Ex. 26                                       Ex. 27                                             Ex. 28    ______________________________________    Craft Copolymer:    Example 17   203.3    Example 18           203.3    Example 19                   203.3    Example 9                          200    Example 11                               200    Deionized water                 16.4    16.4    16.4  13.0  13.0    Basonat ™ PRL 8878X                 24.05   24.05   24.05 24.5  24.5    PMA          6.25    6.25    6.25  12.5  12.5    Results    Viscosity 1 day                 367     1880    1392  1625  gel    Viscosity 14 days                 186     1720    2070  3440  gel    Hardness 1 day                 100     74      127   74    98    Hardness 14 days                 141     113     152   119   140    % NCO remaining    1 day        15      29      45    26    28    14 days      0       0       21    0     0    ______________________________________

Those skilled in the art will no doubt be able to compose numerousvariations on the themes disclosed, such as changing the amounts ofingredients insignificantly from those shown, adding innocuous orsupplementary substances, or substituting equivalent components forthose shown. Such variations are considered to be within the inventiveconcept, as defined in the following claims.

What is claimed is:
 1. A coating composition, useful as a pigmentedbasecoat or a clearcoat for coating a substrate, which compositioncomprises:(a) a binder comprising:5to 98 percent, based on the weight ofthe binder, of a graft copolymer having a weight average molecularweight of 3000 to 500,000 comprising:(i) 2 to 98 percent by weight ofthe graft copolymer of a polymeric backbone of polymerized ethylenicallyunsaturated monomers; and (ii) 98 to 2 percent, by weight of the graftcopolymer, of a macromonomer attached to said polymeric backbone at asingle terminal point of said macromonomer, said macromonomer having aweight average molecular weight of 500-30,000 and comprising 10 to 100percent, by weight of the macromonomer, of polymerized alpha-betaethylenically unsaturated monomers all having carboxylic-acidfunctionalities or all having amine functionalities, the macromonomercomprising methacrylate monomeric units having been reacted in thepresence of a cobalt chelate chain transfer agent; (b) 2 to 50 percent,by weight of the binder, of a crosslinking agent; and (c) 40 to 90percent by weight, based on the weight of the composition, of an aqueouscarrier comprising 80 to 100 percent water; wherein said graft copolymeris the reaction product, in the aqueous carrier comprising 80 to 100percent water, of said macromonomer and said ethylenically unsaturatedmonomers comprising said backbone, wherein at least a portion of thecarboxylic-acid or amine functionalities of said macromonomer has beenneutralized, and wherein the macromonomer is dissolved or dispersed inthe aqueous carrier to stabilize a portion of the graft copolymer thatforms an insoluble particle.
 2. The composition of claim 1, wherein saidmacromonomer comprises between 10 and 40% by weight, based on the weightof said macromonomer, of polymerized ethylenically unsaturated monomerscontaining carboxylic-acid functionality.
 3. The composition of claim 1,wherein said macromonomer comprises between 10 and 40% by weight, basedon the weight of said macromonomer, of polymerized ethylenicallyunsaturated monomers containing hydroxyl functionality.
 4. Thecomposition of claim 1, wherein said backbone is predominantlypolymerized acrylate or styrene, or a combination of acrylate andstyrene.
 5. The composition of claim 1, wherein (i) is polymerizedt-butylamino ethyl methacrylate and (ii) is polymerized methacrylicacid.
 6. A process for preparing a binder for a coating compositioncomprising a graft copolymer which has a polymeric backbone having aplurality of macromonomer arms attached thereto, the macromonomer armshaving carboxylic-acid, or amine functionalities for stabilizing thegraft copolymer in aqueous solution, the process comprising:(a)preparing macromonomers in a solvent by polymerizing, using a cobaltchain transfer agent, a mixture of ethylenically unsaturated monomerscomprising from 10 to 100% by weight, based on the weight of saidmacromonomers arms, of ethylenically unsaturated monomers all containinga carboxylic-acid functionality or all containing an aminefunctionality; (b) neutralizing the macromonomers; (c) dispersing ordissolving the neutralized macromonomers in an aqueous carriercomprising 80 to 100 percent water; and (d copolymerizing 2-98 percentby weight of said macromonomers with a blend of 98-2 percent by weightof alpha-beta unsaturated monomers such that said macromonomers areincorporated into the backbone at a single terminal point of saidmacromonomers, such attachment to said backbone occurring by thereaction of a terminal ethylenic unsaturation on each of saidmacromonomers with the monomers which polymerize to form said backbone,to thereby form the graft copolymer with a weight average molecularweight of 3000-500,000 in said aqueous carrier.
 7. The composition ofclaim 1 wherein said polymerized ethylenically unsaturated monomers ofsaid polymeric backbone are selected from consisting of alkyl acrylates,cycloaliphatic acrylates, aryl acrylates, styrene, alkyl styrene, andmixtures thereof.
 8. The composition of claim 7 wherein said alkylacrylates, cycloaliphatic acrylates and aryl acrylates have up to 12carbon atoms.
 9. The composition of claim 1 wherein said macromonomer ispredominantly polymerized from methacrylate monomers.
 10. Thecomposition of claim 1 wherein said composition is free from asurfactant.
 11. The composition of claim 1 wherein said polymericbackbone of said graft copolymer is provided with a plurality of saidmacromonomers attached thereto.
 12. The binder made in accordance withthe process of claim 6.